Insect and Spider Identification: Wasp on a mission, 1 by ViburnumValley

ViburnumValley wrote:
I wouldn't have believed it, had it not happened right in front of me.

I was potting up some viburnums (imagine that!) when I noticed this wasp-like creature flitting about, and than landing on the ground. Looking closer, I saw that this flying insect had quite a catch that it was hauling (in reverse) over quite a bit of territory - and at a rapid rate for the relative size. I only had time to focus for two images before these were gone up in the bushes (bigger viburnums, natch).

Who might this wasp (or imitator) be?